TIG welding torch

ABSTRACT

A TIG (Tungsten Inert Gas) welding torch (10) comprises a torch body (22), a collet (38a,b,c) for retaining a tungsten rod, and a back cap (42), in which the collet 838a,b,c) passes through an aperture in the torch body (22) from the front of the torch body (22) to the rear of the torch body (22), and is joined directly to the back cap (42) by a screw thread (40a,b,c), the collet (38a,b,c) being drawn backwards against a front section of the torch body (22), to close the collet (38a,b,c) and retain the tungsten rod when the screw thread (40a,b,c) is tightened.

CROSS REFERENCE TO RELATED APPLICATION

This application is a PCT National Phase application based on PCTApplication No. PCT/GB2017/051747 filed on Jun. 15, 2017, which claimspriority of Chinese patent application No. 201610416879.7 filed on Jun.15, 2016, and Chinese patent application No. 201610417070.6 filed onJun. 15, 2016, all of which are incorporated herein by reference intheir entirety.

The present invention relates to a TIG (Tungsten Inert Gas) weldingtorch.

BACKGROUND TO THE INVENTION

TIG welding uses an electrical arc between a non-consumable tungstenelectrode and the metal workpiece to produce a weld. Normally, a fillermetal is used and this is manually fed along the weld. A weldertherefore holds the welding torch with the tungsten electrode in onehand and the filler metal in the other hand. The welding torch includesthe means to deliver a shield gas around the weld site, to avoidoxidisation of the workpiece and poor-quality dross-filled welds. TIGwelding is used to achieve high-precision welds.

In known welding torches, a ceramic nozzle is provided at the front ofthe torch, around the electrode. The purpose of the nozzle is to directthe shield gas to the weld site, where it is required to ensure ahigh-quality weld. Typically, the ceramic nozzle is provided with aninternal screw thread, which corresponds with an external thread on themetal collet body, to hold the nozzle onto the front of the torch.

Often the limit on the longevity of the ceramic nozzle is that the screwthread becomes ‘gritty’ and eventually no longer corresponds properlywith the screw thread on the collet body. It is difficult to achieve agood manufacturing tolerance and the ceramic nozzles do not last a longtime.

TIG welding torches typically include a hollow back cap to protect theback of the tungsten rod. Although in principle the tungsten is not“consumable” in the same way as the welding rod in MIG welding, thetungsten rod will gradually be used up over time, and so typically rodsare supplied in lengths of around 150-200 mm, and a rod will be fedslowly forward in the welding torch during its lifetime. The welder willchoose the length of tungsten he wants to protrude from the front of thetorch, depending on the particular operation being carried out. A colletin the welding torch holds the tungsten rod in its desired positionduring use. Typically, the collet is tightened by compressing itlengthways between a metal collet body with a closed front end from thefront, and a back cap which screws on from the rear. Typically, both themetal collet body at the front and the back cap will attach withstandard right-hand screw threads. As a result, the collet is subject totwisting during tightening. Over time, this damages the collet andlimits its life.

The back cap must be sealed against the rest of the torch when attached,to prevent leakage of shield gas out of the back of the torch. This istypically achieved by providing an O-ring on the back cap, which sealsagainst a seat on the torch body. Again, high precision manufacture isrequired to ensure sealing. Any damage can cause leakage of gas from theback of the torch and again this limits the longevity of the back capand the torch body.

During use, the frontmost parts of the welding torch will get very hot.The tip of the tungsten itself, the front of the collet body, and theceramic nozzle are directly exposed to the heat from welding. This heatis gradually conducted into the torch body and handle. As the handleheats up, it will become uncomfortable and unsafe to continue weldingand the welder must stop to allow the equipment to cool. The shield gashas some cooling effect in addition to its shielding purpose, and someTIG welding torches are water cooled by a continuous flow of waterthrough the body of the torch. However heat still limits the length oftime a welder is able to continuously work.

It is an object of the invention to provide a TIG welding torch withbetter cooling performance and which uses parts that are longer lasting.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, there is provided a TIGwelding torch comprising a torch body, a collet for retaining a tungstenrod, and a back cap, in which the collet passes through an aperture inthe torch body from the front of the torch body to the rear of the torchbody, and is joined directly to the back cap by a screw thread, thecollet being drawn backwards against a front section of the torch body,to close the collet and retain the tungsten rod when the screw thread istightened.

Screwing the collet directly onto the back cap, and tensioning thecollet longitudinally to close the collet, reduces the possibility ofdamage caused by torsion which is characteristic of known designs wherethe collet is tightened by compression from opposing screws at eitherend.

Preferably, a slot and key arrangement is provided between the colletand the torch body, to prevent rotation of the collet with respect tothe torch body when the collet is inserted into the torch body. Thisensures that the collet can easily be closed only by turning the backcap screw. The slot and key is preferably provided on a rear section ofthe collet, as close as possible to the screw which connects the colletto the back cap, or even on the screw itself. This provides a reactionto the twisting forces from the screw, at a point close to the screwlongitudinally, to further avoid twisting along the length of the screwwhich would be caused by relying on reaction at the front of the collet.Also, the slot and key allows adjustment of the tungsten rod to takeplace at a high temperature without having to disassemble the front ofthe torch.

The front section of the torch body may have an interior taper, and theoutside of the collet may have a corresponding exterior taper, so thatthe collet is closed to grip the tungsten rod as it is drawn backwardsby tightening of the back cap.

It has been found that an optimal angle for the tapers is around 30degrees, e.g., between 25 and 35 degrees, most preferably between 28 and32 degrees, 29 and 31 degrees, or 30 degrees to the nearest degree. Thisoptimal angle provides much easier release when disassembly is required.

Preferably, an undercut is provided in the collet forwards of the taper,so that the front of the taper on the collet can be fully inserted intothe torch body, for example by around 1 mm. In front of the undercut ashoulder may be provided which prevents the collet from being furtherdrawn backwards into the torch body when it is already fully closed.This avoids overtightening and ensures that there is always sufficientspace for the required shield gas to flow through the collet.

Preferably, the collet includes a heat sink section where it passesthrough the torch body when fitted. The heat sink section includescooling channels for allowing a cooling gas or liquid to conduct heataway from the collet, during use. In both gas-cooled and liquid-cooledembodiments, the cooling channels substantially improve the coolingperformance and result in a lower-temperature handle, allowing a welderto work for longer without having to wait for equipment to cool.

The collet is preferably made from brass. Typically in known designs thecollet and collet body are made from copper. However, conduction of heatinto the handle is reduced by using brass, further helping to keep thehandle cool in use.

An integrated gas lens may be provided around the front of the collet,and may be retained in the undercut between the tapered section and theshoulder. Providing a gas lens to better direct the flow of shield gasis well known, but in known designs the gas lens has to be fitted infront of the collet and the length of the torch is necessarilyincreased. Providing a gas lens integrated around the front of thecollet is possible in this arrangement where the collet is thefront-most metallic part, and allows the overall length of the torch tobe retained whilst realising the advantages of a gas lens. A slightlywider ceramic nozzle may however be required to accommodate theintegrated gas lens.

According to a second aspect of the invention, there is provided a TIGwelding torch including a torch body and a back cap, the back cap beingattachable to the torch body by a screw thread, the torch body beingovermoulded with a resilient material and the back cap including atapered front section for interfacing with and sealing against theresilient overmoulding of the torch body.

The back cap may be directly attachable to the torch body by a screwthread, as is known in the prior art, or alternatively might beindirectly attached, for example by screw threading to a collet insertedthrough the torch body from the front, per the first aspect of theinvention.

The seal between the back cap and the torch body is found to be moreeffective, reliable and long-lasting for preventing leakage of shieldgas than the known technique of using an O-ring seal.

The overmoulding may be a heat-resistant silicone-based material. Themain body of the back cap may be made from a heat-resistant phenolicbased material.

According to a third aspect of the invention, there is provided a TIGwelding torch including a torch body, a metallic front section forholding a tungsten rod and conducting electricity to the tungsten rod,and a ceramic nozzle for surrounding the metallic front section,characterised in that a heat isolation spacer is provided between themetallic front section and the ceramic nozzle, the heat isolation spacerbeing attached to the metallic front section at a rear end of themetallic front section and a rear end of the heat isolation spacer, andthe heat isolation spacer extending forwards of the attachment, spacedfrom the metallic front section, and the ceramic nozzle being in contactwith the heat isolation spacer forward of the attachment when theceramic nozzle is fitted and the torch is ready for use.

The heat isolation spacer is provided between the metallic front sectionof the torch and the nozzle, the nozzle bearing against the outside ofthe heat isolation spacer when fitted.

Preferably, the metallic front section includes a cooling passage forallowing a cooling gas or fluid to flow, the cooling passage extendingto a longitudinal point corresponding to the point of attachment betweenthe heat isolation spacer and the metallic front section. Alternativelya thermal break may be provided in the form of a hollow wall in themetallic front section.

The heat isolation spacer is ideally made from a material withrelatively low thermal conductivity. For example, stainless steel hasbeen found to be suitable. Stainless steel has a lower thermalconductivity than brass and copper, which are the typical materials forthe metallic front section. Preferably, the heat isolation spacer istapered inwardly towards the front of the torch. The ceramic nozzle mayalso have a tapered interior profile.

The tapered heat isolation spacer ensures that the nozzle is heldcentrally and in a stable position relative to the metallic frontsection of the torch.

Preferably, the heat isolation spacer is attached to the metallic frontsection of the torch by means of a screw thread. The heat isolationspacer may be screwed up to meet a shoulder on the metallic frontsection. In some embodiments, the screw thread and the shoulder are theonly points of contact between the heat isolation spacer and themetallic front section of the torch. The heat isolation spacerpreferably extends forwards, beyond the screw thread. Preferably, atleast two thirds of the length of the heat isolation spacer extends infront of the screw thread. However, the section of heat isolation spacerin front of the screw thread is ideally spaced from the metallic frontsection by, for example, around 0.5 mm, so there is no direct contact.

Longitudinal slots may be provided along the part of the heat isolationspacer which extends forward of the screw thread. The longitudinal slotsallow the heat isolation spacer to be compressed slightly when theceramic nozzle is positioned over the heat isolation spacer. Whencompressed the heat isolation spacer will bear outwardly on the ceramicnozzle from the inside of the ceramic nozzle. The ceramic nozzle istherefore retained by the heat isolation spacer, gripping the nozzlefrom the inside. The part of the heat isolation spacer which extends infront of the screw thread, when formed with slots, in effect is a seriesof leaf springs which push against the inside of the ceramic nozzle andgrip against the internal surface of the ceramic nozzle.

A band made from an elastic material may be provided, one end of theband being stretched around a front end section of the torch body, andthe other end of the band being stretched around a rear section of theceramic nozzle, for providing a gas-tight seal between the nozzle andthe torch body.

The band may be made from, for example, silicone. Ribs may be providedon internal surfaces of the band to provide a better grip and a betterseal with the torch body and/or the ceramic nozzle. A rib may beprovided on the front of the torch body, so that when fitted a rib onthe inside of the band sits behind a rib on the outside of the torchbody. A rib may similarly be provided on the outside of the ceramicnozzle if required. Preferably, the front exterior part of the torchbody which includes the rib and interfaces directly with the band ismade from silicone, or some other heat resisting material.

Using a spacer (and possibly a band) to retain the ceramic nozzle ontothe torch body has advantages over the known method of using a screwthread, because it provides better thermal performance. Also, theceramic nozzle may last longer since minor damage which might preventproper operation of a screw thread will not prevent proper retention ofthe ceramic nozzle by the heat isolation spacer.

It will be appreciated that many embodiments will include features frommultiple aspects of the invention.

DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention, and to show more clearlyhow it may be carried into effect, preferred embodiments will now bedescribed with reference to the accompanying drawings, in which:

FIG. 1 is a perspective view of a liquid-cooled TIG welding torchaccording to the invention, including three different options for thecollet, heat isolation spacer, nozzle and band;

FIG. 2 is a perspective view of the back cap of the TIG welding torch ofFIG. 1 ;

FIG. 3 is a perspective view of two different options for the heatisolation spacer of the TIG welding torch of FIG. 1 ;

FIG. 4 is a perspective view of a collet which is part of the TIGwelding torch of FIG. 1 ;

FIG. 5 is a perspective view of a collet with an integrated gas lenswhich is an alternative option for the collet of the TIG welding torchof FIG. 1 ;

FIG. 6 is a cutaway view of the TIG welding torch of FIG. 1 , showingliquid and gas flow channels; and

FIG. 7 is a cutaway view of a gas-cooled TIG welding torch according tothe invention, fitted with the integrated gas lens collet of FIG. 5 .

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring firstly to FIG. 1 , a liquid-cooled TIG welding torch isindicated generally at 10. The torch is shown in a disassembled state,and three different options of the collet, nozzle, heat isolation spacerand band are shown.

The torch includes a torch body 12. The torch body includes an interfacesection 14 for attaching the torch to a welding machine. The interfacesection 14 includes a cooling liquid inlet 16 and a cooling liquidoutlet 18, and a shield gas inlet 20. The liquid inlet and outlet 16,18and the gas inlet 20 are all copper tubes. The copper tubes are brazedto a brass body 22. The copper tubes and the brass body together form agood electrical conductor, and so can also be used to electricallyconnect the welding torch to the welding machine, so that voltage can besupplied to the torch to strike an arc and make a weld.

The brass body extends along the neck section 24 and head 26 of thetorch 10. The brass body 22 is overmoulded with an insulating material,for example silicone rubber. The neck section 24 includes a locationformation 28 for a moulded handle in the form of an insulated casing(not shown in the drawings). The insulating casing may be rigid plasticand may be, for example, snapped or screwed together over the bottompart of the neck section of the overmoulded brass body 22. Theinsulating casing 28 extends from the neck section 24 to form a handleon the welding torch.

The brass body 22 in the head section 26 is hollow, i.e. an aperturepasses all the way through the brass body 22 along the line indicated A.

The frontmost part 30 of the insulated section of the head 26 of thetorch includes a rib 32. The backmost section of the uninsulated(exposed brass) part of the head 26 of the torch includes an externalscrew thread 34.

To assemble the torch, one of the heat isolation spacers 36 a, 36 b, 36c is screwed onto the screw thread 34 on the front of the brass body 22.One of the collets 38 a, 38 b, 38 c is then passed through the centre ofthe heat isolation spacer 36 a,b,c, and through the aperture in the headsection 26 of the brass body 22. Each of the collets 38 a,b,c includesan external screw thread 40 a,b,c and this screw thread 40 a,b,ccorresponds with an internal screw thread 44 on the front of the backcap 42. Therefore, the collet 38 a,b,c, torch body 12 and back cap 42can all be held together by screwing the internal thread 44 of the backcap 42 onto the external thread 40 a,b,c of the collet 38 a,b,c.

When the collet is fitted, a band 46 a,b,c can be stretched around thefrontmost insulated section 30 of the torch body 12. A rib 32 on thetorch body assists with retaining the band 46 a,b,c onto the torch body12, and preferably the band 46 a,b,c also has one or more internal ribs.A nozzle 48 a,b,c can then be fitted over the heat isolation spacer 36a,b,c. The nozzle 48 a,b,c will be centred and held by the heatisolation spacer 36 a,b,c. The front part of the band 46 a,b,c isstretched over a rear section of the nozzle 48 a,b,c. At least one rib(not visible in the drawing) is provided on the inside of the band 46a,b,c which assists with gripping of the band around the back part ofthe ceramic nozzle 48 a,b,c. In some other embodiments, rib(s) may alsobe provided around the outside of the back of the nozzle.

Nozzles can be of a variety of shapes, sizes, diameters and lengths tosuit specific welding requirements.

FIG. 2 shows the back cap 42 in more detail. The back cap is elongateand hollow, so that it can retain the back part of a tungsten rod. It isopen at the end facing the torch body 12 in use (the bottom end in FIG.2 ). The back cap is made from plastics, and has a brass threaded insert50 at the open end. The exterior of the open end is tapered. The taperangle α is preferably 30 degrees.

The tapered front section of the back cap 42 forms a seal against thesilicone overmoulding of the torch body 12, when the torch is assembled.The silicone overmoulding of the torch body 12 for this reason extendssubstantially behind the brass body 22 of the head 26 of the torch. Backcaps can be supplied in a variety of lengths and are easilyinterchangeable on the torch to suit different requirements, for examplerestricted access to the weld site may require a shorter back cap.

FIG. 3 shows the heat isolation spacers 36 a,b. Each of the heatisolation spacers is made from stainless steel, and each issubstantially in the form of a tapered elongate shell which is widetowards the rear (towards the top of the FIG. 3 drawings) and narrowertowards the front. Longitudinal slots 52 extend from the front of eachheat isolation spacer, along for example two thirds of the length of theheat isolation spacer. The slots are equally spaced around thecircumference of the heat isolation spacer, for example five slots maybe provided spaced by 72 degrees. The stainless steel leaves defined bythe slots form leaf springs, and so when the nozzle 48 a,b,c is pushedonto the front of the heat isolation spacer 36 a,b,c the leaves willdeform inwardly, but push outwardly onto the inside surface of thenozzle 48,a,b,c, holding the nozzle in place on the heat isolationspacer. Each of the heat isolation spacers 36 a,b includes an internalscrew thread 54, near the rear end of the heat isolation spacer. Theinternal screw thread 54 corresponds with the screw thread (34, FIG. 1 )on the brass body 22 of the head 26 of the torch, so that the heatisolation spacer may be screwed onto the brass body 22. The heatisolation spacer is designed to provide a thermal break between thenozzle and the body 22, thus preventing heat generated from the weldingprocess from being transmitted to the body 22.

FIG. 4 shows the collet 38 c in more detail. The collet comprises a rearattachment section 56, a central heat sink section 58 and a front gripsection 60. The rear attachment section 56 includes the external screwthread 40 c which corresponds with the internal screw thread on thethreaded insert (50, FIG. 2 ) of the back cap (42, FIGS. 1,2 ). Also, alongitudinal slot 62 extends from the rear of the collet 38 c, cuttingthrough the screw thread and terminating in front of the screw thread 40c. A rib 64 is provided at the end of the screw thread, and the slot 62passes also through the rib 64. The rib 64 provides a shoulder to limithow far the collet 38 c can be screwed into the back cap (42).

The slot corresponds to the position of a pin which extends from theinside wall of the hollow brass body of the torch head (26). As thecollet 38 c is passed through the aperture in the brass body, the pinslides into the slot 62. The pin and slot 62 prevent rotation of thecollet 38 c with respect to the brass body (22). This ensures that thecollet 38 c can be tightened onto the back cap (42) simply by holdingthe torch (for example by its handle) and rotating the back cap (42).

The heat sink section 58 of the collet 38 c includes spines 65, andchannels 61 running between the spines 65. In use, shield gas passesthrough the channels 61 on its way from the gas inlet (20) and out ofthe front of the nozzle (48 c). This assists with cooling the torch.

The front grip section 60 of the collet 38 c is the part which grips thetungsten rod when the collet 38 c is closed. A tapered section 66 isprovided, which is wider towards the front of the collet 38 c andnarrower towards the rear. In use, the tapered section 66 passes intothe front of the aperture in the brass body (22) of the head (26) of thetorch. As the collet 38 c is drawn backwards by tightening the screwthread 40 c onto the back cap 42, wider and wider parts of the taperedsection 66 are drawn into the aperture in the brass body (22) of thehead (26). This closes the jaws of the collet 38 c to retain thetungsten rod. Preferably, the front opening of the aperture in the brassbody (22) is internally tapered to match the taper 66 of the collet 38c. The jaws will therefore move from fully open to fully closed on veryslight movement of the collet 38 c from an open position where the frontedge of the tapered section 66 is just in line with the opening of thebody (22) of the head (26), to a closed position where the front edge ofthe tapered section 66 is recessed within the opening of the body (22)of the head (26) by for example 0.5 mm. In front of the front edge ofthe tapered section 66, an undercut 68 is provided. The undercut 68,together with longitudinal slots 70 through the tapered section 66,provide gas flow channels to allow shield gas to flow from the channels61 of the heat sink section 58, through the front of the collet 38 c andout of the nozzle.

FIGS. 5 a and 5 b show an alternative collet 38 b. The collet 38 b againhas an attachment section 56 and a heat sink section 58. These parts aresubstantially identical to those of the collet 38 c in FIG. 4 . The gripsection 60 likewise includes a tapered section 66, an undercut 68 andlongitudinal slots 70. However, this alternative collet 38 b is providedwith an integrated gas lens 72. The gas lens 72 is of a known type—aseries of meshes provided in the path of the shield gas serves to directthe shield gas, ensuring more uniform flow and better weldingperformance. The gas lens 72 is integrated into the collet. This is doneby providing circumferential slots around the jaws of the collet.Internal rings on the gas lens assembly 72 are retained in thecircumferential slots. This allows the gas lens to be fitted around thejaws of the collet, which means there is no increase in the length ofthe torch when fitted with a gas lens. This allows the advantages of thegas lens to be realised without making the torch long and cumbersome.

FIG. 6 shows the welding torch of FIG. 1 , when fully assembled. Partsof the torch are cut away so that gas and liquid flows can be seen.

The band 46 c is seen fitted in FIG. 6 , providing a gas-tight sealbetween the nozzle and the torch body. The band 46 c is shown incross-section, and internal ribs on the band are visible, both where theband 46 c contacts the torch body and where the band contacts the nozzle48 c.

At the back of the torch body, a pin 63 is visible. The pin 63corresponds with the slot (62) in the collet 38 c, to prevent the collet38 c from rotating with respect to the torch body when it is fullyinserted into the aperture in the torch body. Also clear from FIG. 6 isthe extent of the silicone overmoulding behind the brass body 22 of thetorch head 26. The silicone overmoulding extends behind the brass body22 by almost the extent of the tapered section of the back cap 42. Withthe back cap 42 fully tightened onto the collet 38 c, the taperedsection of the back cap 42 forms a gas-tight seal with the siliconeovermoulding of the torch head 26, preventing any leaking of shield gasout of the back of the torch.

The front section of the brass body 22 of the torch is also shown incross-section, and the tapered entrance which corresponds to the taperedsection 66 of the collet 38 c is visible.

The flow of inert shield gas through the welding torch 10 is indicatedby arrows. From the end of the inlet tube 20 at the top of the neck (tothe left of FIG. 6 ), shield gas flows in the channels (61) of thecollet 38 c, between the collet 38 c and the inside wall of the brassbody of the torch head 26. The gas then flows through the slots (70) inthe jaws of the collet 38 c, and then out of the small gap between thecollet 38 c and the front edge of the brass body 22, at the very frontof the undercut (68) in the collet 38 c. The gas is then directedtowards the workpiece by the nozzle 48 c.

The brass body 22 of the head 26 of the torch 10 has a hollow wall. Thisforms a liquid-filled jacket which allows cooling liquid to pass fromliquid inlet 16, into the hollow wall of the brass body, and then out ofthe liquid outlet 18. The liquid jacket is indicated at 74.

The heat isolation spacer 36 c is shown installed on the torch with thethread 54 screwed onto the brass torch body 22. It is apparent from thecross section in FIG. 6 that the heat isolation spacer 36 is only incontact with the brass body at the thread 54, and just to the rear ofthe thread. The parts of the heat isolation spacer 36 c which areforward of the thread 54 are spaced from the brass body 22. This reducesheat transfer from the nozzle into the brass body. It will also be notedthat the small part of the brass body which is in contact with the heatisolation spacer is substantially centrally disposed relative to thehollow wall section, which is cooled by liquid. These features increasethe time for which welding can be carried out before the handle of thetorch becomes hot.

FIG. 7 shows the gas-cooled version of the torch of FIG. 6 . Again,arrows show the flow of gas through the torch. The gas flow is identicalto that in the torch of FIG. 6 , passing through the channels in thecollet 38 b, and then out of the front, directed by the nozzle. Thegas-lens version of the collet 38 b is fitted in FIG. 7 , but equallythe collet 38 c without the gas lens could be fitted to the gas-cooledtorch 10′.

The construction of the brass body 22 of the torch 10′ is again almostidentical to that of torch 10. The brass body 22 still has a hollowwall, although no liquid flows within the cavity. Instead, the hollowcavity 75 in the brass body 22 forms a thermal break, insulating theoutside of the brass body from the inside. This reduces heat transferfrom the nozzle 48 b, which is closest to the hot workpiece, into thebrass body 22 and then to the handle of the torch 10′. Again, the heatisolation spacer 36 b is only in contact with the brass body 22 over avery small area, and the area of contact is substantially central on theextent of the hollow thermal break 75.

The torches 10, 10′ retain the nozzle 48 a,b,c using the heat isolationspacer to grip the nozzle from the inside. The nozzles 48 a,b,ctherefore do not require manufacture with a screw thread, whichincreases possible manufacturing tolerances, reduces cost, and improvesdurability. The collet 38 a,b,c will also last longer than in similarknown torches, because it is not subject to twisting forces whentightened. The twisting from rotation of the back cap 42 is resistedvery close to the back cap 42 longitudinally, by the pin 63 in the slot62.

The gas seal at the back of the torch 10, 10′ is also more reliable andlonger lasting than in known designs. The tapered front section of theback cap 42, which seals against the silicone overmoulding behind theback of the brass body 22, provides a high-quality seal.

Finally, the torch 10, 10′ has excellent thermal performance comparedwith known designs. The nozzle is joined to the body of the torch via aheat isolation spacer 36 a,b,c. The heat isolation spacer is made fromstainless steel which has lower thermal conductivity than brass orcopper, and the area of contact between the heat isolation spacer andthe brass body is very small. Furthermore, where the heat isolationspacer does contact the brass body, there is either a thermal break orliquid cooling channel, limiting the heat that is transferred into thehandle of the torch.

The embodiments described above are provided by way of example only, andvarious changes and modifications will be apparent to persons skilled inthe art without departing from the scope of the present invention asdefined by the appended claims.

What is claimed is:
 1. A TIG (Tungsten Inert Gas) welding torchcomprising a torch body, a back cap, and a collet for retaining atungsten rod, the collet including an exterior tapered section which iswider towards a front of the collet and narrower towards a rear of thecollet and a back cap, in which the collet passes through an aperture inthe torch body from the front of the torch body to the rear of the torchbody, the aperture having a front section with an internal tape, and inwhich the collet is joined directly to the back cap by a screw thread,the collet being drawn backwards against a front section of the torchbody, to close the collet and retain the tungsten rod when the screwthread is tightened, and in which a slot and key arrangement is providedbetween the collet and torch body, for preventing rotation of the colletwith respect to the torch body when the collet is inserted into thetorch body.
 2. A TIG welding torch as claimed in claim 1, in which theslot and key is provided on a rear section of the collet.
 3. A TIGwelding torch as claimed in claim 1, in which an undercut is provided inthe collet, forwards of the taper section.
 4. A TIG welding torch asclaimed in claim 1, in which the collet includes a central heat sinksection, the heat sink section including channels allowing gas flow tocool the collet in use.
 5. A TIG welding torch as claimed in claim 1, inwhich an integrated gas lens is provided around the front of the collet.6. A TIG welding torch as claimed in claim 5, in which the gas lens isretained in an undercut forwards of the tapered section of the collet.